1. Field of the Invention.
The subject of the present invention is a device for positioning and locking rods, pins or wires, particularly for an external fixator in the field of orthopaedics. More particularly, it relates to a clamping device used as a support piece in osteosynthesis and osteoplasty to be incorporated into external fixator elements when a bone is fractured.
2. Description of Prior Art.
There are a great many support pieces or clamps on the market for producing fixation assemblies to meet the ever-increasing demands of orthopaedic surgery. Those selected should be those which are more able to fulfil their function through their simplicity and their ease of handling, time being an extremely important factor in such operations. Although external fixators have been in existence for some time, the support pieces are still evolving in order to provide better solutions for various problems often encountered.
U.S. Pat. Nos. 4,784,125 and 5,095,919 relate to a hoop element and also an external fixator in which this hoop element is incorporated with the members for fixing pins and wires intended to be used in osteosynthesis and osteoplasty.
European Patent EP 0 321 472 describes an articulation element for the relative positioning of fixing rods or bone pins of an external fixator. This articulation element comprises a number of pairs of gripping jaws which on the adjacent faces exhibit slots which form a passage intended to accommodate a rod or a pin. The angular position between the said pairs can be locked and there is a tightening element passing through the said pairs of gripping jaws to tightly clamp the rods or pins in a relative position. Furthermore, the gripping jaws which form a pair are equipped respectively with a positioning projection and with a cutout of a complementing shape.
U.S. Pat. No. 5,752,954 relates to an articulation device for components of an external fixator. This device allows for the relative positioning of fixing rods or pins and comprises two pairs of gripping jaws arranged in such a way that an elastic element acts against the gripping jaws and press the adjacent faces of the gripping jaws in order to lock the articulation device. In their adjacent faces, the gripping jaws have slots which are positioned and arranged in such a way to exhibit an opening allowing a rod or pin to be clamped by pressure. The teachings of U.S. Pat. No. 5,752,954 are incorporated herein by reference.
The holding and clamping devices known from the prior art have the disadvantage of not holding themselves in a chosen position when they are attached to rods, bars or pins. The user therefore has to maintain the correct relative positioning of the rods, pins and wires until such time as he performs the tightening or locking operation.
The object of the present invention is to overcome this drawback and to provide a device which holds itself in its assembled position, which can be adjusted, until such time as the assembly is tightened or locked.
The present invention corresponds to a device for positioning and locking rods, pins or wires, particularly for an external fixator in the field of orthopaedics. The device comprises two external jaws and a tightening assembly. The tightening assembly has a connecting element secured to a tightening member. The assembly allows the jaws to form at least one opening exhibiting at least one cavity in the form of a gripping jaw allowing a hoop, a rod, a pin, bar or a wire to be clipped by pressure against the action of an elastic member which keeps the device in position prior to the locking action which is performed using the tightening member.
According to one embodiment, the connecting element is a bushing which passes through the two jaws and can have placed inside it a retained rod which is designed to be locked with the jaws by the tightening member. The elastic member is a spring in the form of a staple connecting the two jaws, at the opposite side of which is the clipping or gripping zone which has the opposing clamping faces; it may be a single or double spring. The free ends of the staple forming the spring are introduced into orifices in the jaws. According to another embodiment, the elastic member is an axial tension or coil spring. In both embodiments, the two jaws have assembly notches which position them relative to one another.
The jaws and the bushing have devices which prevent one from rotating relative to the other. The upper jaw member has a conical recess and a cylindrical bore for accommodating the bushing, the lower jaw having a bore which has two opposed flat surfaces to play a part in mating with the bushing, the latter having two opposed flat surfaces in its central part in the direction of its axis which correspond with those of the lower jaw member to make it easier to fit into the said lower jaw face.
The bushing, which is cylindrical, has an upper part in the form of a truncated cone with slots in the direction of its axis to allow the rod to be clamped tightly once it has been placed inside it. The bushing has its lower part threaded with a diameter appropriate to that of the tightening nut.
According to another embodiment, the connecting element is a shank passing through a ring connected to a rod, the upper jaw being placed at one of the ends of the shank, around which the lower jaw and the tightening nut are positioned.
According to this same embodiment, the two jaws exhibit an opening in the form of a gripping jaw with at least one cavity allowing a pin or a wire to be clipped and then clamped within the jaws. The two jaws have balls made of a hard material placed alternately between the cavities to assist with locking the wire housed inside it.
The nut is advantageously produced in the form of a ribbed knob screwed around the lower part of the shank which allows the entire device to be kept assembled. A toothed annulus is inserted between the ribbed or knurled knob and the post to set the angular position of the device which will thereafter remain locked once the ribbed knob has been tightened. The device comprises an axial helical spring between the ring and the toothed annulus.
According to a third embodiment, the connecting element is in the form of a bolt, the free end of which is threaded to screw into a bore in the post, the bolt passing through a clamp delimiting at least one gripping jaw in the form of a slot placed transversely with respect to the connecting element, the material placed between the bottom of the slot and the external surface of the clamp acting as a spring.
According to any one of the embodiments, the device is able to act as a support piece for an external fixator comprising a circular or part circular hoop formed from a bar of specified cross-sections, pins, bars or wires or rods, in which fixator the devices exhibit outer openings allowing the clipping of the hoop, of the pins and of wires and the fixing of the rods or of the said devices by their posts so that by tightening the devices, it is possible to achieve relative positioning thereof prior to locking.